My Prototype iMac G4 "Q26" (DVT #6) [No Boot - Help!]

Discussion in 'PowerPC Macs' started by kbfr08, May 4, 2010.

  1. kbfr08 macrumors 6502

    Joined:
    Mar 16, 2007
    #1
    So, my iMac came today. It's a "Q26" DVT Prototype Model (#006)

    Haven't been able to get it to boot yet, it shows a red light on the underside of the mobo.

    Anyway, I dissassembled it. Here's some specs
    1.25Ghz EVT G4
    17" LCD
    DVDRW "DVR-104PC" Mfr. Date: April 2002
    40GB WD HDD, blanked
    No RAM pre-installed (1GB now)
    DVT Bluetooth Adapter

    Everything else is standard AKAIK


    I've attached some photos, I'll upload the rest to an image sharing site.


    If you could help me boot this, I'd appreciate it.
    No HDD Spin (Unless IDE is Unplugged)
    Fans spin at low RPM
    Black Screen - Sometimes Gray for a few seconds
    No Chime - Unless the heatsink is off or reseated
    PMU Reset doesn't help
    I've heatgunned the mobo already
    Checked most chips + capacitors
    Red LED is on on the bottom of the mobo
    No AirPort card, so that wouldn't be a problem.
    Tried reseating the modem and all cables
     

    Attached Files:

  2. ReanimationLP macrumors 68030

    ReanimationLP

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    #2
    Try pulling and replacing the battery.

    Also check to see if your RAM is good or not on another machine.
     
  3. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #3
    Did that, I took the heatsink off, put arctic silver on, and replaced the heatsink and it made a chime and went back to being broken.
     
  4. Hrududu macrumors 68020

    Hrududu

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    Central US
    #4
    Can't say I'm exactly sure what's wrong with your iMac, but I can tell you for sure the red light at the bottom isn't due to a problem. If lit, its simply showing the power is on. If I were to take a guess, I would say there is a power supply problem due to you not getting any POST error beeps, and the fact that you're not getting power to your HD. This leads me to believe its not a problem with RAM, processor, or logicboard.
     
  5. millar876 macrumors 6502a

    millar876

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    #5
    i take it you have put a system install/restore cd into the drive, and are trying to startup whilst pressing "c" on the keyboard. if your not doing this, that could explain why nothings happening. keep in mind if it as a prototype youll probably need to get Mac OS 9.1 or 9.2 up and running first, then try and update the firmware to allow for osx installation.
     
  6. 666sheep macrumors 68040

    666sheep

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    Poland
    #6
    Hi,
    on your first picture i see that CPU core has crushed corners. Especially lower and upper left. It could be source of your problem. Can you post more detailed picture of CPU core (try to clean rest of thermal paste to make edges better visible)?
     
  7. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #7
    I'll try but the only camera that I own w/ a macro setting is my cell phone.
     
  8. MacTech68, May 5, 2010
    Last edited: Jul 30, 2014

    MacTech68 macrumors 68020

    MacTech68

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    Location:
    Australia, Perth
    #8
    Nice. I like the "Sample" stamp on the CPU.

    Interesting that you had a chime after re-fitting the heatsink.

    A warning that you should never run these for very long unless the logicboard heatsink is re-attached to the faraday cage (the dome).

    I would try removing the RAM altogether, both internal slot and bottom SO-DIMM slot and then try. If you then get error beeps, that should indicate that the CPU is actually OK.

    If it doesn't at least give you error tones with the hard drive, optical drive, bluetooth board, all RAM, modem card and external devices removed then it's like finding a needle in a haystack. You can also remove the battery completely for testing.

    Unfortunately, the bluetooth board is on the underside of the logic board. Take care with the 2 grey thermal pads underneath. They are supposed to be replaced if you take the logic board out but you'll probably get away without replacing them.

    You'll need to keep the display interconnect cable and the fan/speaker/inverter cable connected. They're the two smaller ones next to the IDE connectors, (as well as the power connector of course) making a total of 3 cables to keep connected as a minimum.

    EDIT:
    Interestingly, it seems all but the last two boards were labeled as 820-1501

    iMac (17" 1Ghz)
    Feb 2003 9.2.2, 10.2.3 6H58
    PN 661-2795 = 1Ghz 17" USB 1.0 PC2100 DDR266 RAM

    iMac (USB 2.0)
    Aug 2003 9.2.2, 10.2.7 Build 6R42
    PN 661-2768 = 1GHz 15" USB 2.0 PC2700 DDR333 RAM
    PN 661-2954 = 1.25Ghz 17" USB 2.0 PC2700 DDR333 RAM

    iMac (USB 2.0)
    Oct 2003 9.2.2, 10.3 Build 7C9
    PN 661-2968 = 1GHz 15" USB 2.0 PC2700 DDR333 RAM
    PN 661-2999 = 1GHz 15" USB 2.0 PC2700 DDR333 RAM
    PN 661-2954 = 1.25GHz 17" USB 2.0 PC2700 DDR333 RAM

    EDIT---- still unsure about the 820 numbers for these:
    PN 661-3001 = 1.25GHz 17" USB 2.0 PC2700 DDR333 RAM 820-1550
    PN 661-2989 = 1.25GHz 20" USB 2.0 PC2700 DDR333 RAM 820-1599
     
  9. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #9
    After removing all of the ram, I heard a beep. When replaced the ram and I heard a chime. However, still no HDD nor backlight. When I pulled the plug out and tried to boot again, nothing happened. I've noticed that I can turn the screen and HDD on by unseating the base ram, and inserting half of the stick and shifting it to the right or left; still no chime, though.

    I'm using DDR333 CL2.5 ram, is that the correct type?\

    EDIT:
    The mac has not once output power to usb devices (even when it chimed), so I can't enter any key codes.
     
  10. MacTech68, May 5, 2010
    Last edited: Jul 30, 2014

    MacTech68 macrumors 68020

    MacTech68

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    Australia, Perth
    #10
    The RAM should be fine but I suspect that at least ONE fault is poor RAM connectivity. This will cause all sorts of problems such as intermittent failure to power on, hard freezes (cursor locks on screen) and kernel panics.

    You'll need to clean the edge fingers of the RAM module and the socket.

    The test method I use is to allow the machine to boot (at least until you can see a cursor on the screen) and move the mouse pointer whilst rocking the RAM module from side to side. If the mouse cursor freezes, or you get a kernel panic, you need to clean again.

    Some contact cleaners simply aren't good enough and the machine will be doing it again after a few days. Methods for cleaning vary. Some say you should only ever use a rubber (eraser) on the gold contacts. Some recommend contact cleaners, some recommend alcohol swabs, some say isopropyl alcohol.

    If you look at the edge fingers and see slightly darker gold in places, these can be chemical discoloration from contaminants such as finger prints. In the most extreme/stubborn cases, I've used a used piece of the finest grit "wet & dry" sandpaper and very lightly to "buff" up the edge fingers and slot contacts. Some might find that unbelievable, but from an old tech, sometimes it's the only way other than replacing the socket and it works for many years. :eek:

    I've solved many a mysteriously mis-behaving Mac using this simple test. :eek:
     
  11. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #11
    Cleaned both the ram, and the socket and still no POST. It didn't POST without ram anyway. I've noticed that when I press down on the cpu, there is no 'static' on my headphones (plugged into the 3.5mm jack) but if I don't press on it, there is static. I don't know if that is relevant, but whatever.
     
  12. MacTech68, May 5, 2010
    Last edited: Jul 30, 2014

    MacTech68 macrumors 68020

    MacTech68

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    #12
    Hmmm... it's hard to say. Being BGA (Ball Grid Array), the CPU may have over-heated at some point and cracked some solder joints under the CPU. Or, it could simply be that placing pressure there flexes the whole board.

    At this point, it's really hard to say and getting BGA components checked or "re-balled" is VERY expensive and specialist work. You could try a more aggressive approach to cleaning the RAM socket, but I'll make no guarantees.

    These CPUs get very hot in a matter of seconds without a well attached heatsink. That's why so much attention has to be paid to re-applying transfer compound to the CPU AND the two points on either end of the heatsink that touch the upper dome.

    The only other thing to check might be if the heatsink is contacting tracks on the logic board. I can't recall if there are tracks UNDER the heatsink (at the "chunky" ends). If there are, some kapton tape or other insulating sheet might help. Clutching at straws now.
     
  13. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #13
    I left the computer on for about 10 minutes, rebooted and the screen came on, displayed the a solid gray screen and then immediately turned off. Still no hard drive spin up or USB :/
     
  14. Jacob Wall macrumors newbie

    Joined:
    May 4, 2010
    #14
    That is a lot of thermal paste, you should use less next time.

    I can't however think as to why it won't do what it's supposed to do.
     
  15. kbfr08 thread starter macrumors 6502

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    #15
    That's the thermal paste that apple applied.
     
  16. MacTech68, May 6, 2010
    Last edited: Jul 30, 2014

    MacTech68 macrumors 68020

    MacTech68

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    #16
    When it was on for 10 minutes, I take it there was no display?

    It turned itself off, or you did?

    How warm was the heatsink?

    Did it chime when you rebooted?

    The non-working USB reminds me of one other 1.25Ghz G4 iMac I had in the workshop once. It started with intermittent kernel panics and then the USB died but it ran fine. Once the MacOS USB drivers loaded the USB ports worked fine but there was no going into Startup Manager (Option), Open Firmware (Apple Option O F ) or zapping PRAM (Apple Option P R).

    Quite odd, then it died completely IIRC. I never had it in for long enough and at the time, an exchange logic board was way too expensive for the customer.

    I wonder if the onboard regulation was at fault or if the CPU was slowly killing itself. The failed USB (only on cold boot) should be an indicator - but of what?

    I wonder about the on board regulators (the main PSU only supplies 12V to the motherboard) and all those horrible surface mount electrolytics that are known to fail.
     
  17. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #17
    When it was on for 10 minutes, I take it there was no display? Yep

    It turned itself off, or you did? I turned it off.

    How warm was the heatsink? ~100 Degrees F

    Did it chime when you rebooted? Nope
     
  18. MacTech68, May 6, 2010
    Last edited: Jul 30, 2014

    MacTech68 macrumors 68020

    MacTech68

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    #18
    Well, like I said in the above post, my suspicion would be on-board voltage regulators (the cpu requires 3.3v and 1.8v IIRC) you'd also find 5V, and those electrolytics. Of course, checking the output of the main PSU (12v) would be a good start.

    Logic boards are relatively cheaper than they were, and the logic board is worth more to me to look at (like the "Sample" stamp on the CPU) than in an assembled machine.

    I guess it depends on what you want to achieve vs time, effort, skill & money required to achieve it (obviously).

    I'd love a large, 4Mpixel, detailed, full size picture of the entire logic board for my library if that were possible....... :D
     
  19. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #19
    I don't have an voltage tester to test the psu, is there any other way to test for 12v?

    Also, when the iMac is completely assembled, the cpu heatsink (barcode side) causes a short. I'll also see if I can recover any logs from the hard drive that might tell me what the issue is.

    I'll try to get the picture, but the only camera I have is a HP r742 w/o a macro setting, and my cell camera.

    Btw, I would have already bought a new logic board if using a g4 imac was an interest, I'm much more interested in using the prototype.
     
  20. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #20
    Here's a few more pics of the cpu. I think that's gold on the edges :(
     

    Attached Files:

  21. 666sheep macrumors 68040

    666sheep

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    #21
    http://home.earthlink.net/~strahm_s/manuals.html#imcs - your's is usb 2.0
    In service manual you will find voltage check points, but you will need mutlimer too... :(

    Edit: on first pic CPU core looks damaged (pretty hard, i think). Iv'e seen many "lightly crushed" G4 CPUs that ran without troubles, but your's looks hard damaged to me. But if it chimed... it's meaning only that POST is passed... once. Chime means that logic board recognizes all components like RAM, CPU, graphics card but does not mean that those components are fully working.
     
  22. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #22
    Actually, I can't even get it to chime anymore.

    Anyone want to trade mobos - 17" 1.25GHz needed???
     
  23. MacTech68, May 6, 2010
    Last edited: Jul 30, 2014

    MacTech68 macrumors 68020

    MacTech68

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    #23
    Errr I can see what is wrong. Compare the first image of the CPU with the latter ones. You've removed the insulating sheet from the CPU. That's a no-no with 74xx CPUs. The six little rectangles actually have different voltages on their silver edges. The heatsink shorts them out.

    If you can find a supplier of Mica Washers/Insulators that are large enough to cut a rectangular hole in to expose the centre large rectangle, you'll be able to resolve that problem (unless that insulator you removed is still intact and re-fit-able.

    Your best bet might be eBay for a logic board. You might also be able to sell this logic board as a collector's item with the "SAMPLE" stamp on the CPU.

    Or, search for the part numbers (661-xxxx) earlier in the thread for parts suppliers.
     
  24. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #24
    The insulating sheet was on until I removed the heatsink a few hours ago to take a better pic of the cpu. While troubleshooting, the sheet was on.
     
  25. kbfr08 thread starter macrumors 6502

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    Mar 16, 2007
    #25
    I saw that the usb host controller had a bulge in it today. I checked my mac mini, which uses the same usb controller chip from NEC, and there's no bulge.
    Also, D26 had a hole in it, it's something to do with the audio ports.

    Someone was kind enough to send me the schematic for the prototype, so I'm going to use the serial download port to check for life.

    BTW, D23 was a 15V SOT23 3 prong thingy (D for diode?). It would be great if someone could send me a few ;)

    Also, i think it could use a new voltage regulator. It's labeled sc2602s, I couldn't find this chip on any other mobo, so I could use a few.
     

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